Optical switches

ABSTRACT

Optical switches are described herein. In one embodiment, an exemplary optical switch includes, but is not limited to, a first waveguide, a second waveguide across with the first waveguide in an angle to form an intersection, and a pair of electrodes placed within a proximity of the intersection to switch a light traveling from the first waveguide to the second waveguide, where the intersection includes a geometry that supports single and multimode propagation. Other methods and apparatuses are also described.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/215,068, filed Aug. 29, 2005 now U.S. Pat. No. 7,397,989, whichclaims the benefit of U.S. Provisional Application No. 60/611,927, filedSep. 21, 2004, which is incorporated by reference herein by itsentirety.

FIELD OF THE INVENTION

The present invention relates generally to fiber optics. Moreparticularly, this invention relates to an optical switch.

BACKGROUND OF THE INVENTION

Integrated optical switches have been widely used recently. To divertlight from one waveguide to another, the waveguides are coupled byspecific geometric arrangements of the two waveguides in relation toeach other, where the coupling is modified by local electro-opticalmanipulation of their indices of refraction. Typical examples ofelectro-optical switches include the Mach-Zehnder interferometer 2×2switch, the directional coupler 2×2 switch, the modal-interference 2×2switch (e.g., two-mode interference switch, bifurcation optical activeswitch), the mode-evolution 2×2 switch, the imbalanced y-branch 1×2switch, the digital-optical switch, and the total internal reflection(TIR) X-switch. Depending on the voltage applied to such switches or insome cases the electrical current actually, light is thus partly orcompletely diverted from an input waveguide to an output waveguide.

By appropriately combining waveguides and switches, a switch fabric(also referred to as switch matrix) is formed to switch light frommultiple input waveguides among multiple output waveguides. A variety ofswitch fabric geometries have been used. Switch fabrics based ongeometries such as crossbar geometry can be used to divert input signalsto output channels arbitrarily. Signals from any input channels can bedirected to any output channel, and even to multiple output channels, inbroadcast and multicast transmission modes.

A typical switch employs the thermo-optic effect in a localized mannerto control the refractive index within polymer waveguide structures toswitch and attenuate the optical signals, which may limit the switchingspeed of the switch. Further, there has been a lack of commerciallyavailable switches possessing microsecond operation that have integratedvariable optical attenuators and integrated optical power monitoring.The lack of integrated power monitoring means external components arerequired, which makes the overall approach more cumbersome and bulky.

SUMMARY OF THE INVENTION

Optical switches are described herein. In one embodiment, an exemplaryoptical switch includes, but is not limited to, a first waveguide, asecond waveguide across with the first waveguide in an angle to form anintersection, and a pair of electrodes placed within a proximity of theintersection to switch a light traveling from the first waveguide to thesecond waveguide, where the intersection includes a geometry thatsupports single and multimode propagation. Other features of the presentinvention will be apparent from the accompanying drawings and from thedetailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 is a block diagram illustrating an exemplary optical switchfabric according to one embodiment of the invention.

FIG. 2 is a diagram illustrating an exemplary layout of an opticalswitch matrix according to one embodiment of the invention.

FIG. 3 is a diagram illustrating an exemplary switching performance of aswitch matrix according to one embodiment.

FIG. 4A is a diagram illustrating a plot of the real and imaginary partsof the refractive index change as a function of carrier densityaccording to certain embodiments.

FIG. 4B is a diagram corresponding propagation loss as a factor ofcarrier density.

FIG. 5A is a block diagram illustrating a conceptual experiment of TIRaccording to one embodiment.

FIG. 5B is a plot of the reflectivity of a step-index boundary withrespect to FIG. 5A.

FIGS. 6A and 6B are block diagrams illustrating exemplary opticalswitches having electrodes according to certain embodiments of theinvention.

FIG. 7 is a plot illustrating an exemplary performance of opticalswitches shown in FIGS. 6A and 6B.

FIG. 8 is a diagram illustrating an exemplary waveguide cross-section ofan optical switch according to one embodiment.

FIGS. 9A and 9B are diagrams illustrating contour plots of the profilesfor the semi-vector TE and TM fundamental modes.

FIG. 10 is a diagram illustrating propagation computed using the beampropagation method (BPM) according to one embodiment.

FIG. 11 is a diagram illustrating definitions uses for IL, isolation,and crosstalk according to certain embodiments.

FIG. 12 is a block diagram illustrating exemplary x and asymmetricy-branch switches according to certain embodiments.

FIGS. 13A and 13B are diagram illustrating numerical simulation resultsaccording to certain embodiments.

FIGS. 14A and 14B are diagrams illustrating the numerical predictionsfor a ridge waveguide according to one embodiment.

FIG. 15 is a block diagram illustrating a physical model for the 2×2 TIRX-switch according to one embodiment of the invention.

FIG. 16 is a diagram illustrating exemplary results of a BPM simulationof propagation according to one embodiment.

FIG. 17A is a diagram illustrating light loss due to a variety offactors.

FIG. 17B is a diagram illustrating an exemplary optical switch accordingto one embodiment.

FIG. 18A is diagram illustrating an exemplary performance of an opticalswitch according to one embodiment.

FIG. 18B is a diagram illustrating an exemplary optical switch accordingto one embodiment.

FIG. 19 is a diagram illustrating an exemplary electrode configurationsused in an optical switch according to one embodiment of the invention.

FIG. 20 is a diagram illustrating an exemplary optical switch accordingto one embodiment.

FIGS. 21A and 21B are diagrams illustrating an exemplary optical switchaccording to another embodiment.

FIGS. 21C-21I are diagrams illustrating various configurations ofoptical switches according to certain embodiments.

FIGS. 22A and 22B are diagrams illustrating an exemplary optical switchhaving VOA capability according to one embodiment.

FIGS. 23, 24A, and 24B are plots illustrating performance of opticalswitches according to certain embodiments.

FIGS. 25A and 25B are diagrams illustrating an exemplary optical switchhaving a tap capability according to another embodiment.

FIG. 26 is a plot illustrating performance of optical switches accordingto one embodiment.

FIG. 27A is a diagram illustrating an exemplary optical switch accordingto another embodiment.

FIG. 27B is a plot illustrating performance of optical switchesaccording to one embodiment.

FIG. 28 is a diagram illustrating an exemplary structure of an opticalswitch according to one embodiment.

FIG. 29 is a diagram illustrating an exemplary geometry of the ridgeregion and the slab region of the waveguide according to one embodiment.

FIGS. 30 and 31 are diagrams illustrating performance of certainformulas according to certain embodiments.

DETAILED DESCRIPTION

Optical switches matrix are described herein. In the followingdescription, numerous specific details are set forth (e.g., such aslogic resource partitioning/sharing/duplication implementations, typesand interrelationships of system components, and logicpartitioning/integration choices). However, it is understood thatembodiments of the invention may be practiced without these specificdetails. In other instances, well-known circuits, software instructionsequences, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.Rather, in particular embodiments, “connected” may be used to indicatethat two or more elements are in direct contact with each other (e.g.,physically, electrically, optically, etc.). “Coupled” may similarly meanthat two or more elements are in direct contact (physically,electrically, optically, etc.). However, “coupled” may alternativelymean that two or more elements are not in direct contact with eachother, but yet still co-operate or interact with each other.

FIG. 1 is a block diagram illustrating an exemplary optical switchfabric according to one embodiment of the invention. Referring to FIG.1, exemplary switch fabric 100 includes, but is not limited to, anoptical switch matrix (also referred to as an optical switch array) 102having multiple switching elements to receive multiple input opticalfibers 101, one or more variable optical attenuators (VOAs) 103, and oneor more photonic detectors 105 to monitor, via one or more tapmechanisms 104, the optical signals traveling along multiple outputoptical fibers 106.

In one embodiment, the switch matrix 102 may be an 8×8 switch matrixthat routes any one of the optical signals received by the input fibers101 to any one of the output fibers 106 using multiple optoelectricalswitches, such as, for example, directional couplers, BOA couplers,digital-optical-switches, and X or Y switches. In a typical embodiment,the switches (also referred to as optical cross-connect switches,switching elements, switching nodes, and/or switches) employed in theexemplary switch matrix 102 may be able to perform one microsecondoperation (or shorter in time) with fully integrated variable opticalattenuation and output optical power monitoring, which enables constantoutput power operation over multiple channels. In one embodiment, theswitches employed within the switch matrix 102 may be manufactured usinga semiconductor material (e.g., silicon or the like) and localmanipulation of the refractive index by the carrier-induced plasmaeffect generated by appropriately placed electrodes and current injectedfrom the application of a forward-biased voltage (closely related arethe Pockels and Kerr effects that rely upon strong electric fieldsrather than strong electrical currents).

The switches may possess multiple functionality, such as, for example,attenuation, and power monitoring, etc. For example, according to oneembodiment, at least one of the switching elements that make up theswitching matrix may be capable of partially switching to divert aportion of an optical signal to one output port while routing theremaining portion of the optical signal to another output port. Notethat although components 102-104 are shown as separate functionalblocks, it will be appreciated that these components are integratedwithin each other on a single substrate (e.g., single integrated chip).

FIG. 2 is a diagram illustrating an exemplary layout of an opticalswitch matrix according to one embodiment of the invention. In thisembodiment, a crossbar architecture is employed. A 2×2 TIR (totalinternal reflection) X-Switch enables directly any of the architecturesthat possess a matrix layout of intersecting “rows” and “columns” ofwaveguides. In a particular embodiment, the exemplary crossbararchitecture is designed based on the TIR X-Switch for a pitch of 127μm, where each switch employs dual electrodes.

FIG. 3 is a diagram illustrating an exemplary switching performance of aswitch matrix according to one embodiment. In this embodiment, as anexample, optical signals are applied to seven of the inputs, but theymay be applied to some or all eight inputs. Note that FIGS. 2 and 3 areshown for illustrating purposes only. The techniques described hereinmay be applied to a variety of switch matrix having different layouts.Further detailed information regarding layouts of a switch matrix may befound in a co-pending U.S. patent application Ser. No. 10/867,948,entitled “Optical Switch Matrix”, filed Jun. 14, 2004, assigned to acommon assignee of the present application, which is hereby incorporatedby reference.

In one embodiment, the main portion of the physical design is awaveguide chip (e.g., planar lightwave circuit). The complete module mayinclude at least one of the following functional elements andattributes:

-   -   waveguide 2×2 switches,    -   waveguide variable optical attenuators (VOAs),    -   low-loss waveguides,    -   low-scatter waveguide crossings,    -   means of tapping the optical signal for optical power        monitoring,    -   integrated photodetectors (end-fire or fiber coupled as        alternatives),    -   multi-fiber optical connections to the multi-waveguide chip,    -   low-loss optical coupling between SMF fiber and the waveguide        chip for input and output,    -   chip-level electrodes and wire-bond pads, including electrical        connects,    -   wire bonds for package-to-chip electrical connects,    -   hermetic package presuming the need owing to integrated        photodetectors, and    -   reliability for telecom applications (e.g., GR-1209 and GR-1221        compliance, operating lifetime of 20 years).        Relatively Large Ridge Waveguide TIR X-Switch

In one embodiment, the simulation work may be performed retied on theSoref model for the magnitude of the real and imaginary parts of therefractive index in silicon that can be changed by the presence ofcharge carriers by current injection. For example, for wavelength λ=1.55micron (μm), for the real part of the refractive-index change, theempirical formula may be illustrated as follows:

$\begin{matrix}\begin{matrix}{{\Delta\; n_{Re}} = {{\Delta\; n_{e}} + {\Delta\; n_{h}}}} \\{= {{{- 8.8} \times 10^{- 22}\left( {\Delta\; N_{e}} \right)} - {8.5 \times 10^{- 18}\left( {\Delta\; N_{h}} \right)^{0.8}}}}\end{matrix} & (1)\end{matrix}$

For the imaginary-index change expressed as a coefficient of inducedabsorption in units of cm⁻¹, the related formula may be illustrated asfollows:

$\begin{matrix}\begin{matrix}{{\Delta\alpha} = {{\Delta\alpha}_{e} + {\Delta\alpha}_{h}}} \\{= {{8.5 \times 10^{- 18}\left( {\Delta\; N_{e}} \right)} + {6.0 \times 10^{- 18}\left( {\Delta\; N_{h}} \right)}}}\end{matrix} & (2)\end{matrix}$FIG. 4A is a diagram illustrating a plot of the real and imaginary partsof the refractive-index change as a function of carrier densitycorresponding to the above two formulas, where Δn_(lm)=Δα(λ/4π). FIG. 4Bis a diagram illustrating a plot of the absorption in units of dB/cm asa function of carrier density corresponding to the above formula (2).

In one embodiments high reflectivity owing to carrier induced indexchange is needed, where the phenomena employed is total internalreflection (TIR). Measurements are performed to measure the reflectivityof a region of high carrier injection, and to use this measurement ofthe reflectivity to infer the magnitude of the refractive index change.FIG. 5A is a block diagram illustrating a conceptual experiment of TIR.The reflection is not anticipated to be 100% as for TIR in a loss-lessmaterial system, but reduced owing to the presence of a carrier-inducedabsorption (e.g., an imaginary-part of the refractive index). The plotof the reflectivity of a step-index boundary is shown in FIG. 5B.Referring to FIG. 5B, the standard Fresnel equations is utilized forspecular reflection, where the required refractive indices of siliconare taken from the above formulas. As shown in FIG. 5B, intensityreflectivity as a function of the angle of incidence approaching grazingincidence (i.e., approaching 90°) upon a step-index boundary ofcarrier-induced index change. Note that the absorption owing to carrierinjection diminishes the reflectivity from demonstrating total internalreflection (TI) within the silicon.

Slab Waveguide with Drive Electrodes

According to one embodiment, electrodes may be used to drive the carrierinjection that have edge field effects which lead to index gradientsrather than the idealized step-index considered in the previoussubsection. In one embodiment, the size scale of these gradients(carrier-diffusion distance) may be designed to match the size scale ofthe fundamental mode as shown in FIGS. 9A and 9B.

The gradients of the index change depend upon the specific geometry ofthe electrode in connection with the geometry of the silicon waveguide.An SOI (silicon on insulator) slab waveguide with coplanar electrodesmay be used in design of the TIR X-Switch. FIG. 6A is a block diagramillustrating an exemplary optical switch having coplanar electrodesaccording to one embodiment of the invention. Note that the size anddimension of FIG. 6A is shown for the purposes of illustration only.Other configurations may be utilized.

Alternatively, parallel-plate electrode geometry as shown in FIG. 6B maybe utilized according to certain embodiments. It is useful to note thatunder simplifying conditions analytic expressions might be developed toapproximate the edge effects (size-scale of the gradients) in theinduced index change, which would further enable simplified technicalspecification of the electrodes and waveguide geometry to produce thephenomena of TIR in silicon.

Referring back to FIG. 5A, according to one embodiment, the grazingangle may be designed with approximately 3° (e.g., 87° angle ofincidence measured from the surface normal), including angles rangingapproximately from 1° to 10°. For any angle of grazing incidence, thereflected optical power depends upon the applied bias voltage or, hence,the carrier density N. As the bias voltage (e.g., carrier density) isincreased, the reflectivity should be seen to increase. High reflection(e.g., “attenuated” TIR) may occur as the bias setting is furtherincreased beyond some characteristic value for the particular angle ofincidence as shown in FIG. 7, which is a diagram illustrating anexemplary plot of intensity reflectivity as a function of the carrierdensity owing to current injection, according to one embodiment.

Relatively Low-Loss Large-Ridge Waveguide Crossing

According to one embodiment, low-optical-loss waveguide crossings aredesigned based upon the use of large ridge waveguides. The waveguidesare weakly guiding for the fundamental optical mode (e.g., the effectivemode index is close to the numerical value for the large-slab waveguidemodes). In one embodiment, the preferred material system is silicon oninsulator (SOI). FIG. 8 is a diagram illustrating an exemplary waveguidecrossing of an optical switch according to one embodiment.

In a particular embodiment, the etch-depth E is approximately 1.5 μm,where this ranges from approximately 3 μm down to 1 μm. In a furtherembodiment, ridge width W may be approximately 10 μm and height H may beapproximately 10 μm. The indices of refraction are the known values forpure materials at a wavelength of approximately 1.55 μm, which persistto be valid for wavelength ranging within the S, C, and LITU-communication wavelength bands for the optical carrier wave. Notethat the parameters used in FIG. 8 are shown for purposes ofillustration only. It will be appreciated that other dimensions and/orconfigurations may also be utilized. FIGS. 9A and 9B are diagramsillustrating contour plots of the profiles for the semi-vector TE and TMfundamental modes.

According to one embodiment, the performance of waveguide crossings maybe designed based upon this specific SOI ridge waveguide. Thepropagation computed using the beam propagation method (BPM) is shown inFIG. 10 according to one embodiment. In BeamPROP™ 5 from RSoft Design,Inc., the selected commercial BPM software, file-power monitors measurethe optical mode power throughout the waveguide crossing. These filepower monitors use the same electric field as is used to form the launchfield for the simulations. The resulting insertion loss (IL) isapproximately 0.21 dB and the isolation is approximately −60.1 dB. Inone embodiment, the isolation may be degraded. The definitions uses forIL, isolation, and crosstalk are shown in FIG. 11.

According to one embodiment, asymmetric y-branches in addition towaveguide crossings may be utilized, as shown in FIG. 12. The numericalsimulation results are shown in FIGS. 13A and 13B for the IL andcrosstalk. As shown in FIGS. 13A and 13B, the IL of the asymmetricy-branches is lower than the IL for a waveguide crossing. The crosstalkfor a waveguide crossing also shows an oscillatory behavior that is notpresent for the asymmetric y-branch. FIGS. 14A and 14B are diagramsillustrating the numerical predictions for the single case of a ridgewaveguide with an etch depth of approximately 1.5 μm. These results wereproduced with a much higher numerical accuracy (closer to convergence),so slight discrepancies are to be noted when compared to the lessaccurate and scalar results shown in FIGS. 13A and 13B.

Switching in Relatively Large SOI Ridge Waveguides

FIG. 15 is a diagram giving the top view of the ridge-waveguide layoutwith three cross-sectional views to further illustrate a physical modelfor the 2×2 TIR X-switch according to one embodiment of the invention.In one embodiment, the BPM is used to simulate the performancenumerically. The model establishes a baseline for the performance ofcarrier-induced TIR X-switches in silicon following the use of a largeridge waveguide.

Referring to FIG. 15, regions (majority of the device) 1501 representsilicon. The regions 1502 corresponding to the location of the driveelectrode have an index of refraction modified by carrier-injection,which is determined by the formulas described above for the real andabsorptive parts of the refractive index, respectively. Note that thelength of the electrode is approximately 1000 μm, and may change invalue depending upon the crossing angle and amount of mode confinement(e.g., mode-profile width).

FIG. 16 is a diagram illustrating exemplary results of a BPM simulationof propagation through the activated switch (e.g., carrier densityN=4×10¹⁸ cm⁻³). The IL is approximately 0.83 dB, where approximately0.64 dB of the IL is due to the presence of carrier-induced absorptionas detailed by the plots as shown in FIG. 17A. FIG. 17A also shows thepresence of the Goos-Hanchen effect, which influences the optimallateral offset of the electrode. It is anticipated that the actualgradients may influence the optimal lateral offset far greater than theGoos-Hanchen effect. Both offset effects may continue to be present. Thegradients may most likely require the electrode to be displaced to theleft of the center of the waveguide-crossing vertex shown in FIG. 15 tosuch an extent that the overall offset becomes positive in value. FIG.17B is diagram illustrating the possible operating states of an opticalswitch according to one embodiment. FIG. 18A is diagram illustrating anexemplary performance of an optical switch having a model similar to theone shown in FIG. 15. Referring to FIG. 18A, transmission (linear scale)normalized to the input intensity of the bar (diverted path) and cross(straight-through path) states of the 2×2 TIR X-switch as a function ofthe carrier density (bias voltage). The results are from the use of both2D and 3D BPM modeling. TE and TM results are both included.

The performance of the TIR Y-Switch depicted in FIG. 18B is anticipatedto be similar to that given in FIG. 18A when regarding the performanceof the straight-through and diverted pathways of the switch.Historically, the naming conventions for the cross and bar states areswapped for the TIR Y-Switch with respect to those for the TIR X-Switch.

Exemplar Electrode Designs

According to one embodiment, relatively long electrodes are used todrive the carrier-induced index changes, which creates a high-reflectionphenomena. FIG. 19 is a diagram illustrating an exemplary electrodeconfigurations used in an optical switch according to one embodiment ofthe invention. Referring to FIG. 19, a large-electrode embodimentincludes the essential doping (n⁺ and p⁺) and metallization that enablesthe fabrication and operation of the TIR X-Switch. The electrodefunction to drive the bar state of operation, but when powered down arealso compatible with the specification of low optical loss for thepassive waveguide crossing (e.g., the cross state of operation). The TIReffect produces optimal switching when the TIR effect is longitudinallyinvariant, which means the TIR mirror is flat. The hatched region 1901in FIG. 19 represents the region of desired carrier-inducedrefractive-index change, which is meant to correspond in width to thatdepicted in FIG. 15. It is denoted this width as W_(elect). In oneembodiment, the carrier injection process leads to gradients of therefractive index owing to carrier diffusion. Coplanar electrode geometrymitigates the effects of diffusion by sharpening the discontinuity(TIR-mirror formation) in the refractive index. Thus, the widthW_(elect) used in the BPM modeling with sharp gradients as depicted inFIG. 15 may be regarded as the effective width owing to the presence ofgradients, not the physical width of the coplanar electrodes.

According to one embodiment, there are two locations for the electrode,either on top of the ridge 1902 (i.e., the zone not etched) or on top ofthe slab 1903 (e.g., etched zone) of the waveguide. Since each electrodeof the pair crosses over the two ridge waveguide forming the waveguidecrossing, each of the electrodes can be consider to be divided into fiveor fewer segments, similar to an embodiment as shown in FIG. 20. Thereare at most two distinct segments on top of the ridge and three distinctsegments located on the slab. A particular case is depicted in FIG. 20,where the n⁺ electrode is composed of five segments and the p⁺ electrodeis composed of four segments. In order to achieve a flat TIR mirror, thedrive signal to each of these segments may need to be tailored. In oneembodiment, this may be achieved by using a voltage divider circuit todivide the drive signal over the electrodes in some prescribed manner orindividual electrical traces may deliver unique drive signals to thefive electrode segments.

Shown in FIGS. 21A and 21B are diagrams of certain embodiments ofoptical switches having of grating-edge profiles in the doping andmetallization and in the doping only, respectively. These edge profilesare on both edges of a given electrode of the actual coplanar pair ofelectrodes. The use of the gratings is to solve a potential problem oftoo much crosstalk (scattered light) in the bar output when the switchis powered down and operating in the cross state. The origin of theincreased signal in the bar output would be reflection off of a weak,but flat, index perturbation owing to the doping profile or inducedstrain in the material, as shown in FIG. 21C. The index difference wouldallow for a reflection to occur that directs the input light to the baroutput, which is not desired for proper function of the TIR X-Switch.

Furthermore, this unwanted weak reflection would direct light to the baroutput similar to the “attenuated” TIR mirror that is established by thepresence of charge carriers owing to an applied bias voltage. Thegrating structure (e.g., non-uniform surfaces or edges) is blazed sothat specular reflection off of the grating would direct the inputlight, not to the bar output, but to a much different angle. The lightwould then diffract away within the stab waveguide. The crosstalk wouldthen be reduced greatly, if present at all. The depth of the gratingnotches is to be much less than the carrier diffusion length(approximately 10 μm), but equal to or longer than the wavelength oflight (e.g., approximately 1.55 μm).

When the electrode is activated via application of a bias voltage, theblurring that occurs from carrier diffusion may effectively remove theinfluence of the grating and the desired TIR switching may occur. Theembodiments may use grating-edge profiles in the doping andmetallization profiles (e.g., FIG. 21A) or in the doping profile only(e.g., FIG. 21B), where a uniform metallization edge-profile would beused in this second case.

Referring to FIG. 21A, the edge of electrode segment showing thepossible use of a blazed grating in the doping and metallizationprofiles. These profiles would be occurring also for the opposite edgeof the electrode segment. Referring to FIG. 21, the edge of electrodesegment showing the possible use of a blazed grating in the dopingprofile and a uniform metallization profile. These profiles would beoccurring also for the opposite edge of the electrode segment.

Some of the attributes of the electrode design may include one or moreof the following:

-   -   Electrode for longitudinal invariant carrier injection to create        a flat TIR mirror;    -   Minimum electrode dimensions for reduced drive power;    -   Silicon doping and metallization consistent with low-loss        optical propagation of a powered down (passive) waveguide        crossing;    -   Ridge waveguide geometries that best enable the TIR switching        while maintaining a low-optical-loss waveguide crossing when        powered down; and    -   Mitigate by electrode and waveguide design the impact of index        gradients and carrier absorption on the reflected light owing to        an imperfect carrier-induced TIR mirror.

In view of the properties of a reflection orating employed in designingthe electrodes with the grating feature, according to one embodiment,the angle of diffraction θ_(m) is related to the angle of incidenceθ_(i) by the following formulaa(sin θ_(m)+sin θ_(i))=mλ  (3)where a is the grating period, λ is the wavelength of light, m=0, ±1,±2, ±3, . . . is the diffraction order. Shown in FIG. 21D is also thedefinition of the grating-surface normal, which the angles are measured.

The case of m=0 corresponds to the case known as zeroth-orderdiffraction when the angle of diffraction θ_(m), is equal to the angleof incidence θ_(i). Zeroth-order diffraction (depicted in FIG. 21E) isindependent of the wavelength λ and grating period a. Note that thiscase is similar to specular reflection as depicted in FIG. 21C in termsof the angular relationship.

According to one embodiment, the diffraction grating can be constructedsuch that the periodic structure has facets at an angle θ_(b), which isknown as the blaze angle as depicted in FIG. 21F. This blazing of thediffraction grating improves the efficiency of higher-order diffraction(m≠0) and decreases the power diffracted in the zeroth order. As aresult, a reflected or diffracted waves may be reduced since it wouldcontribute to the crosstalk of the bar state.

In order to assess what conditions lead to enhanced diffractionefficiency owing to blazing, we first examine the angles of incidenceand reflection for the facets. Specular reflection off of the flatfacets with angular orientation θ_(b) occurs for angles of incidenceθ_(i) and angles of reflection θ_(r) given by the relationθ_(r)+θ_(b)=θ_(i)−θ_(b) when measured with respect to thegrating-surface normal.

When the angle of diffraction θ_(m) matches this angle of facet specularrefection θ_(r), then the diffraction occurs with improved efficiency.The actual efficiency of diffraction cannot be assessed with the currentapproach. However, we can still find the detailed relation among theparameters of wavelength λ, grating-period a, diffraction-order in, andincidence-angle θ_(i). The requirement of simultaneous diffraction andfacet specular reflection in the similar angular direction givesθ_(m)=θ_(r)=θ_(i)−2θ_(b),  (4)where the incidence-angle θ_(i) satisfies the implicit the followingequation2a cos(θ_(i)−θ_(b))sin θ_(b) =mλ.  (5)

These relations give specific conditions for blazed diffraction oncesome of the parameters are fixed. In this case, when the wavelength λ isa communications-channel wavelength, it is useful to consider it as afixed parameter. It can vary, though, with the selection ofcommunications channel. In one embodiment, it is assumed the wavelengthλ to be within the C-band, where it is customary to use the value of1.55 μm as an approximate value for such an analysis. It will be usefulto design the grating for use with a particular diffraction-order m, butmore than one choice is possible and appropriate. In a particularembodiment, it is considered m=1, 2, and 3. The design parametersrequiring determination of proper values are the grating-period a andblaze-angle θ_(b). These two parameters need to correspond to a gratingstructure that can be fabricated as shown in FIG. 21G, according to oneembodiment.

There are two grating structures that we shall consider in detail, whichare depicted in FIGS. 21H and 21I. Note that these configurations areillustrated by way of examples, not by way of limitations. The case inFIG. 21H is a typical case where the grating depth isd=a sin θ_(b) cos θ_(b);  6)whereas the case in FIG. 21I corresponds to the maximum grating-depthd=a tan θ_(b)  (7)

That is possible without having grating facets that overlap likecresting ocean waves. We can solve Eqs. (5) to give us the generalrelation for the grating-period a, which isa=mλ/[2 cos(θ_(i)−θ_(b))sin θ_(b)]  (8)and further use Eq. (7) with Eq. (8) to give a relation between thelargest grating depth and the blaze angle, which isd=mλ/[2 cos(θ_(i)−θ_(b))cos θ_(b)]  (9)

There is a grating-depth d owing to its relation to the characteristiccarrier-diffusion distance, which it is identified to be approximately10 μm. Thus, Eq. (9) can be used to find proper values of theblaze-angle θ_(b) for target values of the incidence-angle θ_(i), wherethe wavelength λ is approximately 1.55 μm. The diffraction order m is afree parameter that provides for the selection of the diffracted waveθ_(m) with blaze-enhanced diffraction efficiency. The correspondinggrating-period a is then found using Eq. (8). Equation (7) is also validfor relation the grating-period a to the grating-depth d and blaze-angleθ_(b).

According to one embodiment, one of the purposes of using the blazedgrating is to move light that would have been specularly reflected at anangle θ_(refl), when incident on a uniform surface at an angle θ_(inc),to a diffracted order with blaze-enhanced diffraction efficiency. Thenet angular displacement is θ_(d)=θ_(i)−θ_(m), where θ_(i) correspondsto θ_(inc), and θ_(inc)=θ_(refl). The appropriate selection of adisplacement-angle θ_(d) reduces the amount of unwanted light fromcoupling to the bar-state when the light is supposed to be directedsolely to the cross state.

Following table illustrates various embodiments of grating-period a andblaze-angle θ_(b) with the resulting displacement-angleθ_(d)=θ_(i)=θ_(m) for the selected diffraction order m optimized underthe assumption of a preferred grating-depth d=10 μm and an operatingwavelength λ=1.55 μm. The use of the “-” is to indicate for that modenumber m there is no good value that may be utilized. Marked in boldfont is believed to be a preferred selection of parameter values. Notethat the influence of blazed-grating electrodes have not been includedin the performance assessment in other sections.

crossing inc. m = 1 m = 2 m = 3 half angle angle a a a θ θ_(i) (μm)θ_(h) θ_(d) (μm) θ_(b) θ_(d) (μm) θ_(b) θ_(d) 1° 89° 166 3.5° 6.9°  71.18.0° 16.0° 44.0 12.8° 25.6° 2° 88° 234 2.4° 4.9°  81.6 7.0° 14.0° 48.111.7° 23.5° 3° 87° 396 1.4° 2.9°  95.7 6.0° 11.9° 53.0 10.7° 21.4° 4°86° 1287  0.4° 0.9° 115.5 5.0°  9.9° 58.9 9.6° 19.3° 5° 85° — — — 145.33.9°  7.9° 66.1 8.6° 17.2° 6° 84° — — — 195.5 2.9°  5.9° 75.3 7.6° 15.1°7° 83° — — — 298.0 1.9°  3.8° 87.3 6.5° 13.1° 8° 82° — — — 624.1 0.9° 1.8° 103.7 5.5° 11.0° 9° 81° — — — — — — 127.4 4.5° 9.0° 10°  80° — — —— — — 164.9 3.5° 6.9°Exemplary VOA Switching Capability

FIGS. 22A and 22B are diagrams illustrating the possible implementationsof the TIR X- and Y-Switches as variable optical attenuators (VOAs).Referring to FIGS. 22A and 228, the cross-state of the TIR X-Switch(bar-state of the TIR Y-Switch) has little or no attenuation(high-transmission) when powered off, which means it is normallytransmitting. The bar-state of the TIR X-Switch (cross-state of the TIRY-Switch) is highly attenuating (opaque) when powered off, which meansit is normally blocking.

Referring to FIG. 22A, two possible implementations of the TIR X-Switchas a VOA: (a) Uses the cross state to provide little or no attenuation(high-transmission) when powered off normally transmitting; (b) Uses thebar state to provide high attenuation when powered off, normallyblocking.

Referring to FIG. 22B, two possible implementations of the TIR Y-Switchas a VOA: (a) Uses the bar state to provide little or no attenuation(high-transmission) when powered off, normally transmitting. (b) Usesthe cross state to provide high attenuation when powered off, normallyblocking.

FIG. 23 shows via the use of a dB vertical scale that the attenuation(IL) of the cross state for the TIR X-Switch (bar-state of the TIRY-Switch) may be higher than the attenuation of the bar state for theTIR X-Switch (cross-state of the TIR Y-Switch). Referring to FIG. 23,the results of FIG. 18A replotted on a dB vertical scale (i.e., IL). Thecross state reaches higher values of IL (attenuation) than the bar statefor the TIR X-Switch, and similar may occur for the TIR Y-Switch (swapthe labeling of the cross and bar states). The results are from the useof both 2D and 3D BPM modeling. TE and TM results are both included.

The critical parameter determining this possibility is theelectrode-width W_(elect), which we examine in FIG. 24A via 2D BPMsimulations of the behavior of the TIR X-Switch. Similar behavior isexpected for the TIR Y-Switch. Referring to FIG. 24A, the plots of thebar- and cross-state transmission (linear scale) as a function ofcarrier density for various values of the electrode-width W_(elect), forexample, 2, 5, 10, 20 μm, from 2D BPM simulations of the behavior of theTIR X-Switch. TE and TM curves are both included.

FIG. 24B illustrates the sensitive dependence of the cross-stateattenuation upon the electrode-width W_(elect). The maximum value ofattenuation reached for the cross state becomes larger than for the barstate for reasonable values of the carrier density when theelectrode-width W_(elect) is made large such as 20 μm. Note that this isalso consistent with efficient switching, where the minimal amount ofgenerated carrier density is required to switch from the cross to thebar state. Referring to FIG. 24B, the plots of the bar- and cross-stateattenuation in dB of the TIR X-Switch as a function of carrier density,which shows the sensitive dependence of the cross-state attenuation uponthe electrode-width W_(elect). These results are from the same 2D BPMsimulations of the behavior of the TIR X-Switch presented in FIG. 24A,where the legend also applies here.

The use of the cross-state output is of interest for some VOAapplications. In the case of forming an N×N Crossbar switch, it is thebar state of the TIR X-Switch (cross state of the TIR Y-Switch) thatforms the switched and attenuated output. It is anticipated that theattenuation provided by the bar state may be sufficient for mosttelecommunications applications. Note that the maximum attenuationcorresponds to the crosstalk of the waveguide crossing with no applieddrive power (e.g., the bias voltage).

Power Tap, VOA, and Switching Capability

The other output port of the TIR X-Switch or TIR Y-Switch can alsofunction as a tap giving the power of the input signal as depicted inFIGS. 25A and 25B. It is required an initial calibration of thepercentage of tapped optical power as a function of the applied biasvoltage (carrier density). Then for any bias voltage, the input opticalpower can be calculated in firmware on the control board or usingadditional software. A limit of such an approach stems from the weakestsignal that is detectable above the noise limit of the photonicdetector.

For the configurations of FIG. 25A (a) and FIG. 25B (a), the drive power(bias voltage) needs to be set high enough in value to achieve asufficiently large tap signal. In order to reduce the optical loss ofthe output in FIG. 25A (a) and FIG. 25B (a) the electrode-widthW_(elect) should be as small as possible as indicated in FIG. 24B yetmaintains the range of attenuation required when also used as a VOA. Forthe configurations of FIG. 25A (b) and FIG. 25B (b), the drive power(bias voltage) needs to be reduced from the large value that switchesthe input to the cross-state output of the TIR X-Switch (bar-stateoutput of the TIR Y-Switch). In order to reduce the loss of the tappedoptical signal of FIG. 25A (b) and FIG. 25B (b), the electrode-widthW_(elect) should again be as small as possible, yet able to provide thedesired switching and/or VOA functionality.

Referring to FIG. 25A, TIR X-Switch is used as a VOA as depicted in FIG.22A with the addition of a tapped output for power monitoring. It isalso appropriate for use in forming an N×N Crossbar switch or N×N MatrixDouble Crossbar switch with variable optical attenuation and powermonitoring. Referring to FIG. 25B, TIR Y-Switch used as a VOA asdepicted in FIG. 22B with the addition of a tapped output for powermonitoring. It is also appropriate for use in forming an N×N MatrixDouble Crossbar switch with variable optical attenuation and powermonitoring.

It is anticipated cases where the tapped signal may be too small to beuseful for certain values of the desired cross- or bar-state output,since the tapped signal is derived from the opposite output port usedfor the VOA/switched output. The two output ports/states are related.

FIG. 26 is a parametric plot of the bar-state output power in dB plottedversus the cross-state output power in dB, where implicitly it is thecarrier-density parameter that is varied. Multiple curves are given,which correspond to cases of different electrode-width W_(elect). Theappropriate electrode-width W_(elect) is the one that matches best theoverall specifications, where a smaller electrode-width W_(elect)improves the performance of the power tap and a larger electrode-widthW_(elect) improves the VOA functionality for certain configurations.

Referring to FIG. 26, parametric plot of the bar- and cross-state outputof the TIR X-Switch on dB scales for various values of theelectrode-width W_(elect), for example, 2, 5, 10, 20 μm. TE and TMcurves are both included.

It is established that the limiting case of the TIR X-Switch as a powersplitter (see FIG. 27A) and compare it to a power splitter with noexcess loss by plotting in FIG. 27B the parametric curves of FIG. 26 ona linear scale. The smaller the electrode-width W_(elect), the closerthe functionality of the TIR X-Switch is to that of a power splitterwith linear transfer function. The TIR X-Switch is lossy, though, andalso asymmetric in loss between the bar and cross states.

Referring to FIG. 27B, it is shown the limit of a loss-less lineartransfer function, which is the limit of a perfect power splitter. It isto be noted that for small values of the electrode width, the efficiencyfor switching is diminished, meaning larger values of carrier densitymay be required to achieve switching with minimum IL. Similar behaviormay occur for the TIR Y-Switch. Parametric plot of the bar- andcross-state transmission of the TIR X-Switch for various values of theelectrode width, for example, 2, 5, 10, 20 μm. TE and TM curves are bothincluded. From large to smaller electrode widths, the transfer functionbecomes progressively more linear, and approaches the functionality of aperfect power splitter (e.g., lossless linear transfer function), wherethe cross-state output corresponds to “output 1” and the bar-stateoutput corresponds to “output 2” in FIG. 27A regardless of employing anX or Y structure.

The electrode-width W_(elect), whether taken to be the actual width ofthe perfect index region in FIG. 15 or taken to be the effective widthof the carrier-injection region, determines greatly the performance ofthe TIR X-Switch for use beyond switching. The electrode-width W_(elect)determines the character of the device as a VOA and as a power tap. Itis this insight that enables the design of the TIR X-Switch in Silicon(SOI) and in other material systems employing similar or differentoptical index control mechanisms. Examples of other embodiments arecarrier injection in InP and GaAs, thermo-optic induced index change inpolymer and silica (glass), electro-optic effect (linear and quadratic)in Lithium Niobate, Lithium Tantalate, Electro-Optic Polymer, and PLZT.

FIG. 28 is a diagram illustrating exemplary geometrical parameters thatdetermine the layout and size of an N×N matrix according to oneembodiment. Referring to FIG. 28, depicted is the case of a 2×2 Crossbarwith coplanar electrodes matched to the vertex length L_(vertex).

FIG. 29 is a diagram illustrating an exemplary geometry of the ridgeregion and the slab region of the waveguide according to one embodiment.The condition developed by Soref [see R. A. Soref, J. Schmidtchen, andK. Petermann, IEEE J. Quantum Electron., v. 27, n. 8, pp. 1971-1974,1991] that predicts the occurrence of single and multimode propagationcharacteristics for large ridge waveguides is

$\begin{matrix}{\frac{W}{H} \leq {\alpha + \frac{\frac{h}{H}}{\sqrt{1 - \left( \frac{h}{H} \right)^{2}}}}} & (10)\end{matrix}$for the case of

$\begin{matrix}{{\frac{h}{H} \geq 0.5},} & (11)\end{matrix}$which is the case we are interested. Note that refractive indices do notenter the formula because of an additional assumption essentially that Hbe much larger than the wavelength. To be clear, the refractive-indexcase we are considering is n_(f)>n_(s) and n_(f)>>n_(c). Thenumerical-value of the dimensionless parameter α has been considered tobeα=0.3, Soref Condition,  (12)α=0.0, Strong Condition.  (3)Soref derives the value of 0.3 for α, but some designers have adoptedthe stronger condition by setting α to zero. FIG. 30 is a diagramillustrating a plot of Eq. (10), but may be regarded for h/H>0.5. Notethe relation E=H−h between the etch-depth E, the ridge-height H, and theslab-height h.

For small crossing angles (i.e., θ<<1 radian), the structure at thewaveguide crossing of a TIR X-Switch has a width of approximately 2Wwhen the ridge waveguides first meet to form a sharp vertex. To insure awaveguide structure with width 2W supports a single mode, according toone embodiment, we take Eq. 3 and replace W with 2W to arrive at a morerestrictive functional condition:

$\begin{matrix}{\frac{2W}{H} \leq {\alpha + {\frac{\frac{h}{H}}{\sqrt{1 - \left( \frac{h}{H} \right)^{2}}}.}}} & (14)\end{matrix}$

The ridge waveguide with width W is far from supporting higher-ordermodes. Eq. 14 also serves as our definition of a “weakly confined” largeridge waveguide that has a large mode profile to form a low-loss andlow-crosstalk waveguide crossing and hence a TIR X-Switch. The plot ofEq. 14 is shown in FIG. 31, where a suitable region about this conditionis indicated. It is to be understood that the desired functionality maypersist for parameter values within this region. The preference, though,is for larger relative values of W, which is to reduce the amount ofdiffraction that occurs within a waveguide crossing. Reduced diffractionmay lead to a further reduction in optical loss and crosstalk.

Referring to FIG. 31, overlay of the plot of the more restrictiveformula given in Eq. 14 assuming α=0.3 for the boundary line, which isgiven by the thick and solid line 3101. The dashed outlined regionindicates the region where the intended performance persists. Thehatch-shaded region 3102 is the preferred region since it corresponds tolarger values of W and hence reduced diffraction within the waveguidecrossing. The region 3103 is the preferred relative value (h/H,W/H=(0.85, 1.0), and the gray squares are additional relative values ofinterest, namely, (0.9, 1.2), (0.8, 0.82), and (0.7, 0.64) according tocertain embodiments.

According to certain embodiments, the design choice available is thenumerical value of the ridge-height H. The numerical value H ofapproximately 10 μm is appropriate owing to it being compatible with thedesign of a large ridge waveguide that couples light efficiently toCorning single-mode SMF fiber. Thus, for H=10 μm, the numerical valuesof interest for (h, W) are approximately (9 μm, 12 μm), (8.5 μm, 10 μm),(8 μm, 8.2 μm), and (7 μm, 6.4 μm), where the preferred values are (8.5μm, 10 μm). The concept persists for various values of H rangingapproximately from 4 μm to 16 μm. For H=4 μm, the numerical values ofinterest for (h, W) are approximately (3.6 μm, 4.8 μm), (3.4 μm, 4 μm),(3.2 μm, 3.28 μm), and (2.8 μm, 2.6 μm), while for H=16 μm, thenumerical values of interest for (h, W) are approximately (14.4 μm, 19.2μm), (13.6 μm, 16 μm), (12.8 μm, 13.1 μm), and (1.2 μm, 10.2 μm). Thisanalysis is the basis for the numbers summarized in a table furtherbelow. It is also useful to make use of the etch-depth ratioE/H=(H−h)/H, but it is should be noted that it is redundant when theslab-height ratio h/H is provided.

Following table illustrates the geometrical implications upon the sizeof a single 2×2 TIR X-Switch.

TABLE 1 Fixed Parameters Dependent Variables W θ Pitch P L_(2×2)L_(vertex) L_(N×N) N (μm) (degrees) (μm) (μm) (μm) (cm) 8 10 1 127 3638573 5.5 8 10 2 127 1818 287 2.7 8 10 3 127 1212 191 1.8 8 10 4 127 908143 1.4 8 10 5 127 726 115 1.1 8 10 6 127 604 96 0.9 8 10 7 127 517 820.8 8 10 8 127 452 72 0.7 8 10 9 127 401 64 0.6 8 10 10 127 360 58 0.5

According to one embodiment, the appropriate electrode length is relatedto the mode-profile width when the mode-profile width exceeds theridge-width W, which corresponds to the case of a weakly confined mode.The maximum electrode length cannot exceed the length of the individual2×2 TIR X-Switches within the N×N matrix prescribed for a particularvalue of the pitch P. Thus, we can take the numerical value of the 2×2length L_(2×2) to be the upper bound of the electrode length L_(elect).The case of W=10 μm is considered in Table 1, where the ratioL_(2×2)/L_(vertex) is approximately 6.4. When examining the other casesof the width W ranging approximately from 2.6 μm to 19.2 μm,L_(2×2)/L_(vertex) are approximately 24.4 and 3.3 respectively.

Note that the TIR X-Switch may have a weak wavelength dependence owingto the small changes in the refractive index (real and imaginarycomponents) in silicon with wavelength. There is no use of interference,which would depend sensitively upon the wavelength of operation andcreate strong wavelength sensitivity. Thus, 2×2 TIR X-Switch may be usedthroughout the fiber-communication wavelengths ranging approximatelyfrom 1300 nm to 1612 nm, which is the typical approximately 1300-nmisolated wavelength and the S (1491.69-1529.55 nm), C (1529.75-1569.59nm), and L (1569.80-1611.79 nm) bands, where C is the most prevalent inuse.

Referring to Table I shown above, length L_(vertex)=W/sin θ of thewaveguide crossing measured from vertex to vertex, which depends on theridge-width W and the crossing half-angle θ; length L_(2×2)=(P/2)/tan θof each 2×2 TIR X-Switch within the N×N matrix, which depends upon thepitch P of the matrix and the crossing half-angle θ; and overall lengthL_(N×N)=(2N−1)L_(2×2) of the N×N matrix, which is given from the case ofN=8. The preferred case is marked in bold.

Following Table II illustrates certain parameters that may be used todesign an optical switch according to certain embodiments of theinvention.

TABLE II Preferred Embodiment Ranges Parameters (approximately)(approximately) Wavelength 1550 nm 1300 nm-1612 nm Ratio h/H 0.850.7-0.9 Ratio W/H 1.0 0.6-1.2 Ridge-Height H 10 μm  4 μm-16 μmSlab-Height h 8.5 μm  2.8 μm-14.4 μm Ridge-Width W 10 μm  2.6 μm-19.2 μmEtch-Depth-Ratio 0.15 0.1-0.3 E/H = (H − h)/H Half Angle, θ (angle from3°  1°-10° z-axis) Thickness of the Wafer 1 mm 0.4 mm-2 mm   SubstrateInsulator SiO₂ 0.4 μm 0.3 μm-1 μm   Coplanar-Electrode/Length L_(elect.)1000  360 μm-3600 μm Ratio L_(elect.)/L_(vertex) 5  1-25 EffectiveElectrode Width W_(elect) 5 μm  1 μm-20 μm Mode-Amplitude In-Plane Full-16 μm  3 μm-32 μm Width at Half-Maximum (approximately) (FWHM) ProfileWidthNote that the parameters shown in Table II are shown for purposes ofillustration only. A variety of different parameters may be utilizeddependent upon different design requirements.

Thus, optical switches have been described. In the foregoingspecification, the invention has been described with reference tospecific exemplary embodiments thereof. It will be evident that variousmodifications may be made thereto without departing from the broaderspirit and scope of the invention as set forth in the following claims.The specification and drawings are, accordingly, to be regarded in anillustrative sense rather than a restrictive sense.

1. An optical switch, comprising: a first waveguide; a second waveguideacross with the first waveguide in an angle to form an intersection; anda pair of electrodes placed within a proximity of the intersection toswitch a light traveling from the first waveguide to the secondwaveguide, wherein at least one electrode has at least one protrogenedge that reflects light; wherein the intersection includes a geometryhaving a ridge width (W), a ridge height (H), and a slab height (h)satisfying the following equation${\frac{2W}{H} \leq {\alpha + \frac{\frac{h}{H}}{\sqrt{1 - \left( \frac{h}{H} \right)^{2}}}}},$wherein α is ranging from approximately 0.0 to 0.3.
 2. The opticalswitch of claim 1, wherein the intersection is formed having a dopingprofile layer and a metallization profile layer.
 3. The optical switchof claim 1, wherein H is ranging from approximately 4 μm to 16 μm. 4.The optical switch of claim 1 wherein a slab height ratio of h/H isranging from approximately 0.7 to 0.9.
 5. The optical switch of claim 1,wherein a ratio of W/H is ranging from approximately 0.64 to 1.0.
 6. Theoptical switch of clam 1, wherein the pair of electrodes have a smallcrossing angle.
 7. The optical switch of claim 6, wherein the smallcrossing angle is less than one radian.
 8. The optical switch of claim1, wherein an electrode length of one of the pair of electrodes isrelated to a mode-profile width, wherein the mode-profile width exceedsW.
 9. The optical switch of claim 1, wherein the first and secondwaveguides form an X-switch.
 10. The optical switch of claim 9, whereina cross state of the X-switch provide little or no attenuation whenpowered off and transmits light.
 11. The optical switch of claim 9,wherein a bar state of the X-switch provide high attenuation whenpowered off and blocks light.
 12. The optical switch of claim 1, whereinthe first and second waveguides form a Y-switch.
 13. The optical switchof claim 12, wherein a bar state of the Y-switch provide little or noattenuation when powered off and transmits light.
 14. The optical switchof claim 12, wherein a cross state of the Y-switch provide highattenuation when powered off and blocks light.
 15. The optical switch ofclaim 1, further comprising: an output port that acts as a tap givingpower of an input signal.